Power semiconductor devices with trench gates have become an industry standard because such devices can provide low on resistance and fast switching of relatively high voltages. In particular, current power MOSFETs (Metal-Oxide-Semiconductor Field-Effect Transistors) with trench gate structures can achieve a breakdown range of 20V to 200V and low on resistance.
Shielded gate or split gate trench MOSFETs, as they are sometimes called, have become the current choice for high performance in low to mid voltage power MOSFET products. U.S. Pat. No. 4,941,026, for example, disclosed a trench power MOSFET with a second gate inside the trench for low ON-state resistance. U.S. Pat. No. 5,998,833 discloses a Trench Power MOSFET with a similar split-gate structure for high frequency switching. U.S. Pat. No. 7,489,011 discloses trench MOSFETs or trench Insulated Gate Bipolar Transistors (IGBTs), which may include an epitaxially-grown field shield region in the trench beneath the gate of a trench MOSFET or IGBT. Reliability implications of shielded gate trench MOSFETs have also been studied, for example, by Zia Hossain et al. (ISPSD 2016, pp. 391-394), Nishiwaki et al. (ISPSD 2016, pp 215-218), Deng et al. (ISPSD 2016, pp. 75-378), and Nishiwaki et al. (ISPSD 2017, pp. 463-466).
The drawings illustrate examples for the purpose of explanation and are not of the invention itself. Use of the same reference symbols in different figures indicates similar or identical items.